Tunable negligible-loss energy transfer between dipolar-coupled magnetic disks by stimulated vortex gyration

Abstract

A wide variety of coupled harmonic oscillators exist in nature. Coupling between different oscillators allows for the possibility of mutual energy transfer between them and the information-signal propagation. Low-energy input signals and their transport with negligible energy loss are the key technological factors in the design of information-signal processing devices. Here, utilizing the concept of coupled oscillators, we experimentally demonstrated a robust new mechanism for energy transfer between spatially separated dipolar-coupled magnetic disks - stimulated vortex gyration. Direct experimental evidence was obtained by a state-of-the-art experimental time-resolved soft X-ray microscopy probe. The rate of energy transfer from one disk to the other was deduced from the two normal modes' frequency splitting caused by dipolar interaction. This mechanism provides the advantages of tunable energy transfer rates, low-power input signals and negligible energy loss in the case of negligible intrinsic damping. Coupled vortex-state disks might be implemented in applications for information-signal processing.

From chaos to selective ordering of vortex cores in interacting mesomagnets

“…A particular core continues to reverse for a characteristic time T that is on the order of the inverse of the mode frequency difference, TB1/Do. An energy transfer mechanism was previously observed in separated dots by Jung et al, 9 where the ground state of only one of the dots was perturbed by a pulsed RF field. This ground-state perturbation introduced an asymmetry in the initial conditions and, hence, the system behaved like coupled harmonic oscillators where the magnetic potential energy of a vortex core was transferred from one dot to the other.…”

“…In a magnetic dot that has a single vortex-state, the eigenfrequency of the gyrotropic oscillations of the vortex core for both directions of the core polarity (p ¼ ±1) is the same. By contrast, in an array of coupled elements, the dynamic dipolar interaction eliminates this frequency degeneracy and results in collective gyrotropic excitations with different eigenfrequencies that depend on both the relative polarities and chiralities of the individual vortices [8][9][10][11] . An array of interacting magnetic dots form a vortex magnonic crystal 12,13 , similar to the case of coupled, uniformly magnetized elements 14,15 .…”

Direct imaging of phase relation in a pair of coupled vortex oscillators

“…In a pair with opposite core polarizations, a beating pattern attributed to the superposition of two characteristic normal modes has been observed after initial deflection of one of the cores. 28,29 A mode splitting has been detected electrically via excitation of one element with an ac current by Sugimoto et al 31 Interestingly, the inverse-sixth power law for the dependence of the frequency shift on the inter-element distance observed in densely-packed arrays 25 and predicted by the so-called rigid vortex model 17 could not be confirmed for a small interelement distance in experiments and micromagnetic simulations on pairs. This has been attributed to a modification of the core trajectories and the magnetization configuration near the edge for strong magnetostatic coupling.…”

“…In densely-packed arrays of permalloy disks, a relative broadening of the absorption peak in broadband ferromagnetic-resonance measurements varying with the inverse-sixth power of the normalized center-to-center distance between the elements 25 and the size of the array 26 has been observed. Stray-field coupled vortex gyrations in a pair of ferromagnetic elements have been demonstrated via time-resolved magnetic transmission x-ray microscopy, [27][28][29] time-resolved photoemission electron microscopy, 30 and electrical measurements. 31,32 The system behaves like damped coupled harmonic oscillators.…”

Coherence and modality of driven interlayer-coupled magnetic vortices

“…As the core precesses, magnetic charges form on the edges of the disc and stray fields associated with these charges have been used to laterally couple neighbouring vortices 17,29,30 . These magnetostatic interactions are long range but weak, and even edge-overlapped direct exchange discs may demonstrate complex nonlinearities 15 .…”